Alcohol alkoxylates are an important class of materials having use in a wide variety of industrial applications, for example as nonionic surfactants. They are typically prepared by the reaction of an alcohol with an alkylene epoxide such as ethylene oxide (i.e. oxirane) or propylene oxide (i.e. 2-methyloxirane) in the presence of one or more catalysts. Compositions prepared by the reaction of an alcohol incorporating a fluorinated alkyl group with an alkylene epoxide (fluoroalkylalkoxylates) are especially useful in several important industrial applications, including use as nonionic fluorosurfactants in the manufacture of PVC films, electrochemical cells, and various photographic coatings.
There are numerous known catalyst systems and processes for the alkoxylation of fluorinated alcohols. Lewis acids have been shown to be effective catalysts, e.g. boron trifluoride or silicon tetrafluoride, alone or in combination with metal hydrides, fluorides, alkyls or alkoxides. Unfortunately, such acidic materials also catalyze side reactions during the alkoxylation, such as dimerization of alkylene epoxides to form dioxanes. The side reactions lead to excess waste generation, product contamination, and higher consumption of reactants, thereby significantly increasing costs and making operation of the processes more difficult. While the use of strong bases as catalysts for the alkoxylation of hydrocarbon alcohols minimizes some side reactions, the use of strong base alone is not satisfactory for alkoxylation of flurorinated alcohols.
A commercially important class of fluoroalkoxylates consists of a mixture thereof derived by the alkoxylation of a commercial mixture of perfluoroalkylethanols having the general structure R.sub.f CH.sub.2 CH.sub.2 OH wherein R.sub.f is a linear or branched perfluoroalkyl group having from 4 to 30 carbon atoms. The mixture of perfluoroalkyl-ethanols is alkoxylated using strong base catalysts, alone or in combination with sodium borohydride. Unfortunately, that alkoxylation process is plagued with variability in respect of reaction rates and induction period which makes commercial manufacture of these fluoroalkoxylates unpredictable and difficult.
It is more convenient and economical to manufacture, store, and ship fluoroalkylalkoxylates in a solution of higher concentration, typically at about 40 percent by weight. In order to achieve this high solution concentration, known fluoroalkylalkoxylates must be dissolved in an organic solvent, such as isopropyl alcohol (IPA), or in a solvent mixture comprising water in combination with one or more of such organic solvents. However, the resulting solution may be flammable or have increased toxicity, and thus be more difficult and expensive to ship and use safely. In addition, the users of said fluoroalkylalkoxylate solutions frequently must remove the organic solvent during their manufacturing operations; this can be expensive and result in increased worker safety and environmental hazards. Even when dissolved in organic solvent mixtures, known fluoroalkylalkoxylates tend to form sediments. Such sediments are not easily filterable, and they tend to form continuously over time, which makes it impractical to remove the sediments from fluoroalkylalkoxylate solutions before shipment to the user. There are other fluoroalkylalkoxylates disclosed in the prior art which have higher water solubility, e.g. those having a large average number of the hydrophilic oxyalkylene groups, typically greater than about 18 such groups. Another example is Fluorotenside FT-219 marketed by Bayer AG; however, the structures of that product and related compositions incorporate additional hydrophilic functional groups, such as sulfonylamido linkages. In addition, a high degree of alkoxylation may result in the fluoroalkylalkoxylate composition forming a gel during preparation that makes them difficult or impossible to use.